1. Field of the Invention
The present invention relates to a starter motor control device for engines, which detects the rotation speed of an ac generator and the like driven by an engine and also detects the energizing state of a starter motor for starting the engine so as to control the energization of the starter motor.
2. Discussion of Background
Such kind of starter motor control devices have been known in e.g. Japanese Examined Patent Publication No. 40698/1979 and Japanese Unexamined Patent Publication No. 9654/1981.
FIG. 2 shows a circuit diagram in one of the conventional control devices. In FIG. 2, a reference numeral 1 designates a storage battery, and a reference numeral 2 refers to a starter motor for starting an engine (not shown).
The starter motor 2 comprises an electromagnetic switch 21 and an electric motor unit 22, and is connectable to the engine through pinion (not shown).
The electromagnetic switch unit 21 includes relay coils 21a and 21b, and a normally open contact 21c. The contact 21c and the electric motor unit 22 make a series circuit, and the series circuit is connected in parallel with the storage battery 1. The negative terminal of the battery 1 is grounded.
A reference numeral 3 designates an auxiliary switch unit which comprises a relay coil 3a and a normally open contact 3b to be capable of interrupting the energization to the starter motor 2. The contact 3b and the relay coil 21a of the electromagnetic switch unit 21 make a series circuit, and the series circuit connected in parallel with the battery 1. The relay coil 21b in the electromagnetic switch unit 21 is connected between the point at which the contact 3b and the relay coil 21 are jointed and the point at which the contact 21c and the electric motor unit 22 are jointed.
The positive terminal of the battery 1 is connected to a movable contact of a key switch 6. The key switch 6 can take three positions, i.e. an off position (OFF), an on position (ON) and a start position (ST). In the off position, the key switch is open. In the on position, it is grounded through a power supply terminal 4a, a resistor 402 in a control device 4 and a Zener diode 401. In the start position, the key switch 6 is connected to the collector of a transistor 410 as a switching element of the control device 4, through the relay coil 3a of the auxiliary switch 3 and an auxiliary switch driving terminal 4d. The Zener diode 401 serves to give a constant voltage source.
The control device 4 is to carry out operation control for the auxiliary switch 3. In the control device 4, voltage dividing resistors 403 and 404 are connected in series between a power supply terminal and grounded. The point at which the resistors 403 and 404 are jointed is connected to the noninverting input of a comparator 409. The resistors 403 and 404 serve to provide a first reference voltage for the comparator 409.
The noninverting input of the comparator 409 is connected to the point at which the contact 3b of the auxiliary switch unit 3 and the relay coil 21a of the electromagnetic switch unit 21 are jointed, through a resistor 405 and a terminal 4e for detecting the conducting state of the auxiliary switch. The resistor 405 is used to detect whether the auxiliary switch 3 is in the conducting state or in the nonconducting state. When the auxiliary switch 3 is in the conducting state, the resistors 405 and the resistor 404 constitute voltage dividing resistors to provide a second reference voltage for the comparator 409.
The noninverting input of the comparator 409 is grounded through a reverse-current prevention diode 406 and a resistor 407. The point at which the reverse-current prevention diode and the resistor 407 are jointed is connected to the inverting input of the comparator 409.
The resistor 407 is in parallel with a capacitor 408. The resistor 407 and the capacitor 408 constitute a discharge time constant circuit.
The output of the comparator 409 is connected to the base of the transistor 410. The transistor 410 is used to drive the auxiliary switch 3. The base of the transistor 410 is connected to the power supply through a base resistor 411. The emitter of the transistor 410 is grounded through a grounding terminal 4c.
A reference numeral 40 designates an F-V converter which detects the rotation pulse of a generator 5 as described later and converts the pulse frequency into a voltage. The output of the F-V converter 40 is connected to the inverting input of a comparator 414.
The noninverting input of the comparator 414 is connected to the point at which voltage dividing resistors 412 and 313 are jointed. The resistors 412 and 413 are connected in series between the power supply and ground. A voltage that is divided by the resistors 412 and 413 is applied to the noninverting input of the comparator 414 to provide a reference voltage for it. The output of the comparator 414 is connected to the base of the transistor 410. The control unit 4 is constituted in this way.
The generator 5 is driven by the engine to provide power for each electric load. The generator 5 comprises an alternator unit 51 and a rectifier unit 52. The rectifier unit 52 has a rotation detecting terminal 4b connected to the input of the F-V converter 40.
In operation, in preparing for starting the engine, the key switch 6 is set to the on position to provide power for the control device 4. At this time, the auxiliary switch 3 has not been energized, so the starter motor 2 has not been driven and the engine remains standstill.
Since the rotation pulse is not given from the generator 5, the output of the F-V converter 40 is at 0 v, which is input into the inverting input of the comparator 414. On the other hand, the noninverting input of the comparator 414 receives the reference voltage given by the voltage dividing resistors 412 and 413, which is set to correspond to a predetermined rotation speed. As a result, the output of the comparator 414 is "high".
The noninverting input of the comparator 409 receives the first reference voltage given by the resistors 403 and 404. On the other hand, the inverting input of the comparator receives a voltage which is lower than the voltage applied to the noninverting input by a forward direction voltage drop (0.6 v) of the diode 409. As a result, the output of the comparator 409 is "high". That allows the transistor 410 for driving the auxiliary switch 3 to conduct.
When the key switch 6 is set to the start position, the power is applied to the relay coil 3a in the auxiliary switch 3. Since the transistor 410 is in conduction at this time, the relay coil 3a is energized to close the contact 3b.
Thus, the starting motor 2 is energized and the pinion of the motor gets into engagement with the flywheel teeth of the engine to start the engine. As a result, the rotation pulse frequency from the generator 5 is increasing to raise the output voltage of the F-V converter 40.
On the other hand, it is detected by the terminal 4e that the auxiliary switch 3 is closed. The noninverting input in the comparator 409 receives the second reference voltage given by the resistors 405 and 404.
The second reference voltage is set to be higher than the first reference voltage given by the resistors 403 and 404. As a result, the capacitor 408 which is connected to the inverting input of the comparator 409 is charged to a higher voltage accordingly. However, the potential difference between the noninverting and the inverting input remains unchanged to maintain the "high" output of the comparator 409.
After that, when the engine reaches the predetermined rotation speed (it means that the engine has completely started), i.e. when the output voltage of the F-V comparator 40 reaches the same voltage as the reference voltage applied to the noninverting input of the comparator 414, the output of the comparator 414 drops to "low" and the transistor 410 is cut off to open the auxiliary switch 3.
As a result, the starter motor 2 is deenergized to disengage the pinion from the flywheel teeth of the engine. This prevents the starter motor 2 from being conversely driven by the engine to be damaged by overrotation.
Now, it will be considered a case where the key switch 6 is returned from the start position to the on position and is set to the start position again before the engine has completely started.
The inverting input of the comparator 409 is held at the higher voltage by the capacitor 408 for the instant the key switch is returned to the on position.
On the other hand, the noninverting input of the comparator 409 is changed to the lower voltage or the first reference voltage given by the resistors 403 and 404. As a result, the output of the comparator 409 drops to "low" to cut off the transistor 410.
After that, the capacitor 408 discharges through the resistor 407. The transistor 410 is held at cutoff until the inverting input of the comparator 409 drops to the first reference voltage or below, which is applied to the inverting input.
The cutoff-state duration of the transistor is determined by CR time constant of the capacitor 408 and the resistor 407. It is generally set to 3-5 seconds which is the time required for the starter motor 2 to cease its inertial rotation.
For the reasons, even if the key switch is set to the start position again during this time, the auxiliary switch 3 is held at the open state to prevent the starter motor 2 from being energized. This prevents the inertially rotating pinion of the starter motor 2 from being damaged due to the engagement with the flywheel teeth of the engine.
In the conventional devices having such structure, even if the starter motor 2 is energized while the starter motor 2 is rotating by inertia, the pinion of the starter motor is prevented from moving into mesh with the flywheel teeth. That, however, requires the terminal 4e for detecting the conducting state of the auxiliary switch. The control device needs totally five terminals including other terminals.
Since, in general, standard connectors have four or six pins, it is necessarily forced to adopt the six pin type of connectors. This is disadvantageous in terms of quality, cost, and the necessity of additional wire-harness.
Although there is proposed an idea of constituting the auxiliary switch 3 and the control device 4 as one unit to compensate for the drawbacks as mentioned above, it must be considered to be necessary to modify the auxiliary switch 3 depending on the power required to the starter motor 2, and to modify each of set values in the control device 4 depending on the engine power.
The control device which is constituted as one body with the auxiliary switch has disadvantage that it is necessary to extremely increase the number of the types to meet plenty of requirements and that it is difficult to standardize the device.
Since the conventional device has the structure as mentioned above, there must be provided the terminal for detecting the conducting state of the auxiliary switch 3 and an additional wire-harness to be connected to the terminal in order to enable to interrupt the energization to the starter motor 2 while the starter motor is rotating by inertia. If the auxiliary switch 3 and the control device 4 are constituted as one unit in order to prevent the terminal and harness from being added, there is disadvantage that it is necessary to increase the number of the types of the device to meet various requirements.